HVAC actuators are used in a wide variety of applications, including but not limited to air dampers, water valves and the like. Typically, an HVAC actuator has a motor that drives a drive train. The drive train often functions as a sort of transmission, turning a low torque, high speed motor output into a high torque, low speed drive train output that is sufficient to open an air damper, a water valve, or the like. In some cases, the motor may be configured to drive the drive train in a first direction to, for example, open an HVAC component and may drive the drive train in a second direction to, for example, close the HVAC component. Such actuators may be rotary, linear or move in some other fashion, depending on the application.
In some cases, an HVAC actuator such as a spring return actuator may have one or more return springs or other bias mechanism that opposes a driving direction of the motor. For example, a spring return actuator may be configured such that the motor drives an HVAC component (e.g. damper) from a closed position to an open position, while a return spring drives the HVAC component from the open position to the closed position. In other cases, a spring return actuator may be configured such that the motor drives an HVAC component from an open position to a closed position, while the return spring or other bias mechanism drives the HVAC component from the closed position to the open position.
HVAC actuators may be used in a variety of environments, and thus may potentially be exposed to large temperature swings. It will be appreciated that in cool environments, frictional forces within the HVAC actuator may increase relative to frictional forces experienced in warmer environments. In some cases, lubricants become more viscous (thicker) at lower temperatures and/or tolerances such as in the bearings may become tighter. As a result, the motor within the HVAC actuator may need additional power to overcome these temperature-related effects. Also, in a spring return actuator, the return spring (or springs) may need to be able to overcome the increased motor resistance. These factors can combine to often increase the package size, product cost and power consumption of an HVAC actuator.
In one example, assume that a particular HVAC actuator has, at room temperature, a power consumption rating of about 5.5 VA. In a cold environment, the same HVAC actuator may have a power consumption of about 6.5 VA because of increased resistances within the HVAC actuator due to the cold temperatures. It will be appreciated that this represents an increase in power consumption of about 18 percent. In another example, assume that a particular spring return actuator has, at room temperature, a back drive motor resistance of 0.1 N·m (Newton·meters) requiring a load of 2 N·m further up the drive train in order to close the device. In a cold environment, the back drive motor resistance may increase to 0.25 N·m, requiring a load of 5 N·m in order to close the device. It can be seen that this would require a stronger or more robust HVAC actuator design, which may include a stronger drive motor, stronger gearing, stronger housing and the like. This can add significant cost.